Chances are the increase is to pay off the debt and get ahead for winter because many companies like you to start at zero in the middle of the summer, build up a bit of a credit, use that up over winter and then get back down to zero by next summer.
So you were right that £28 was not enough and also that £78 is probably too much and the right amount is somewhere in the middle.
However, you knew that £28 pm wasn't enough for your gas use, so will have to pay the debt that has built up somehow.
Have you had a really good review of your finances and sought any help available with the covid impact?
Do you have other debts? Are you sure your account charges you for the overdraft, because I thought that wasn't allowed any more and they were only allowed to charge interest, which should be a lot less than £8 a day unless your overdraft is huge, and then the charge will be due to all the debt, not just the money that was taken for the gas and electricity.
Sounds like you might need to take a step back and look at this issue as part of the whole problem in that, if you can't afford to pay for essentials like your G&E bill, you need to look at your entire budget, reprioritise (increase your income if you can, reduce the cost of essentials, cut down or cut out any non essentials, only pay what unsecured debt you can afford after your basic essentials are covered, and if you still can't make the payments, that's an indication that you might need more formal help).
Start here:
www.moneysavingexpert.com/family/money-help/
Good luck.